just throwing this out there, since it's a common problem from these changing hands so much since the days of commercial operation...
the pins on the through-hole soldered components on the T-unit boards are generally long enough to get bent and touch nearby stuff if the board was set completely flat (meaning the mounting feet were removed) and can short out whatever. I go over them with electric shears, and if they're bent over enough to where you can't cut them without butchering your board, use a small precision flathead to bend them back upright, then cut.
the PLCC sockets (the brown sockets for CPU-ish chips) also have a tendency to crack in the corners, meaning the walls of the sockets don't make good enough contact against the chips.
if your game roms (the ones furthest to the left offset from the rest) have corrosion on the chip legs, use sandpaper on them to make them shiny and good looking again, then reseat those. you also have to make note that you don't reinstall the ROMs backwards, the chips themselves have a U-shaped notch just like the socket, they have to face the same way. if you plugged them in backwards then your roms are toast.
additionally, if the cabinet has the original power supply in it, chances are that could be on its way out too, hence the black screen. I've seen this condition several times on my KI cab before I replaced the power supply. power supply goes into overcurrent protection shutdown, and it's usually caused by the +5 adjustment pot being corroded. you can salvage these in many cases, but you have to turn the knob completely back and forth both ways several times to "clean" it... but doing this, you won't know what the voltage setting will be at when you run it again. you can run the power supply with the JAMMA harness unplugged, but you can't do it for too long, or else you'll burn up a switching power supply. this can happen in as little as 10 seconds, so you'd have to be quick about setting it to about 5.10 before you plug the JAMMA harness back in and fine tune it.
all else fails, you may just have a bad board. that's the nature of the beast.